ACT30 Просмотр технического описания (PDF) - Active-Semi, Inc

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ACT30

High Performance Off-Line Controller ActiveSwitcher™ IC Family

Active-Semi, Inc 

Active-Semi

Pulse Modulation

The PFWM Switching Control Logic block operates

in different modes depending on the output load

current level. At light load, the VVDD voltage is

around 4.75V. The energy delivered by each

switching cycle (with minimum on time of 500ns) to

the output causes VVDD to increase slightly above

4.75V. The FPWM Switching Control Logic block is

able to detect this condition and prevents the IC

from switching until VVDD is below 4.75V again. This

results in a pulse-modulation action with fixed pulse

width and varying frequency, and low power

consumption because the switching frequency is

reduced. Typical system standby power

consumption is 0.15W.

Short Circuit Hiccup

When the output is short circuited, the ACT30

enters hiccup mode operation. In this condition, the

auxiliary supply voltage collapses. An on-chip

detector compares DRV1 voltage during the off-

time of each cycle to 6.8V. If DRV1 voltage is below

6.8V, the IC will not start the next cycle, causing

both the auxiliary supply voltage and VVDD to reduce

further. The circuit enters startup mode when VVDD

drops below 3.35V. This hiccup behavior continues

until the short circuit is removed. In this behavior,

the effective duty cycle is very low resulting in very

low short circuit current.

To make sure that the IC enters hiccup mode

easily, the transformer should be constructed so

that there is close coupling between secondary and

auxiliary, so that the auxiliary voltage is low when

the output is short-circuited. This can be achieved

with the primary/auxiliary/secondary sequencing

from the bobbin.

ACT30

Rev 5, 05-Jun-09

Innovative PowerTM

-6-

ActiveSwitcherTM is a trademark of Active-Semi.

www.active-semi.com

Copyright © 2009 Active-Semi, Inc.

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